The oxygen evolution reaction (OER) and electrochemical ozone production (EOP) attracted considerable attention due to their wide applications in electrocatalysis, but the detailed reaction mechanism of product formation as well as the voltage effect on O₂/O₃ formation still remains unclear. In this work, the density functional theory calculations were used to systematically investigate the possible reaction mechanisms of OER and EOP on the PbO₂ (110) surface, with the possible reaction network involving surface lattice oxygen atoms (LOM) proposed. The results show that the LOM-2 reaction pathway involving two surface lattice oxygen atoms (O_latt) and one oxygen atom from H₂O was the most thermodynamically reactive. Different potential determining step (PDS) was obtained depending on the multiple reaction pathway, and the results show that the facile diffusion of O_latt would proceed the LOM pathway and promote the formation of surface oxygen vacancies (O_vac1/O_vac2). Furthermore, O_vac1/O_vac2 formation on the surface would trigger further reactions of H₂O adsorption and splitting, which refilled the oxygen vacancy and ensured the considerable stability of the PbO₂ (110) surface. Multiple H₂O dissociation pathways were proposed on PbO₂ (110) with oxygen vacancy sites: the acid-base interaction mechanism and the vacancy fulfilling mechanism.